Drug delivery devices allowing for multiple dosing of a required dosage of a liquid medicinal product, such as liquid drugs, and further providing administration of the liquid to a patient, are as such well-known in the art. Generally, such devices have substantially the same purpose as that of an ordinary syringe.
Drug delivery devices of this kind have to meet a number of user specific requirements. For instance in case of those with diabetes, many users will be physically infirm and may also have impaired vision. Therefore, these devices need to be robust in construction, yet easy to use, both in terms of the manipulation of the parts and understanding by a user of its operation. Further, the dose setting must be easy and unambiguous and where the device is to be disposable rather than reusable, the device should be inexpensive to manufacture and easy to dispose.
Pen-type injectors but also other drug delivery devices being inter alia adapted to dispense and/or inject a pre-defined dose of a medicament comprise a dispensing end to be coupled with an injection component, like an injection needle. The dispensing end of the drug delivery which may comprise a cartridge holder therefore features a mechanical coupling to the releasably receive a needle assembly. Typically, the cartridge holder has a threaded socket to threadedly engage with a correspondingly designed needle hub.
In particular with double tipped needle assemblies, the proximal tip of the needle enters the cartridge holder and penetrates a distal seal of a cartridge disposed therein. When not in use, the disposable needle assembly is to be discarded and the cartridge holder section of the drug delivery device is to be protected by a protective cap. Such caps being typically designed to cover the entire cartridge holder comprise an interconnection member to engage with a correspondingly shaped interconnection member of the drug delivery device.
Typically, the releasable interconnection of cap and housing of the drug delivery device comprises some kind of snap-in or clipping feature. Since the drug delivery device is designed and intended for home medication, assembly and disassembly of the cap to and from the housing of the drug delivery device should be easy and should require only minimum pull-off forces. This way, even physically impaired end users or patients are able to put on and to remove the protective cap.
Providing a rather low pull-off or withdrawal force to remove the cap on the one hand enables elderly or mobility impaired persons to remove the cap easily. On the other hand, a cap featuring a low pull-off force may be rather prone to unintentional disassembly. Hence, the cap may automatically and/or unintentionally release. As a consequence, the cartridge holder and the cartridge disposed therein would be no longer protected. Moreover, unintentional release of the cap may also contaminate the cartridge or components of the drug delivery device. In case a needle assembly remains on the distal end of the cartridge holder, unintentional removal of the protective cap may further increase the likelihood of unintentional stitching.
Hence, a rather low pull-off force may be disadvantageous in terms of patient safety. In particular, children or other unauthorized persons may easily remove the cap and may be thereby considerably endangered by the drug delivery device.
One object of the present invention to provide an improved cap assembly for a drug delivery device, which on the one hand is easy to assemble and to disassemble and which, on the other hand can be securely fastened to the drug delivery device. A secure and safe fastening of the cap assembly should increase patient safety. Also, by way of an improved fastening mechanism, unintentional and/or automatic disassembly of cap and drug delivery device should be largely prevented.